A comparative study of confined organic monolayers by Raman scattering and sum-frequency spectroscopy

The structure of a Langmuir-Blodgett (LB) monolayer of Zn arachidate at the solid-solid interface has been studied by Raman scattering and sum-frequency (SF) spectroscopy. The monolayer was confined in the contact between a CaF2 prism and a MgF2 lens at an average pressure of 60 MPa. This is the first report of an unenhanced Raman spectrum of an organic monolayer at the solid-solid interface. The Raman and SF spectra both show that the deposited monolayer is conformationally ordered and that the monolayer retains this order when placed between the prism and the lens. The relative intensity of the Raman spectra of the Zn arachidate monolayer at the CaF2/air and CaF2/MgF2 interfaces can be explained in terms of the strength of the interfacial electric fields. The relative intensities of the SF spectra at the two interfaces cannot be interpreted in this manner. Deviations from the expected intensities are discussed in terms of structural changes in the monolayer, (C) 2000 Elsevier Science B.V. All rights reserved.